The present invention relates to a method for cleaning systems while simultaneously detecting the degree of cleanliness of the system.
So-called “CIP” applications, i.e. for “clean in place” cleaning of, for example, bar or beverage dispensing systems, typically using aqueous solutions of strong oxidizing agents, entail the general problem of detecting the degree of cleanliness of the cleaned system. For this purpose, color-indicators are added to the solutions, which show a color change when exiting the system as long as they contain oxidizable (usually organic) impurities. Here, permanganate is preferably used as the strong oxidizing agent, which simultaneously provides a color-indicator system. In EP 1,343,864 A1 and EP 1,730,258 A1 (corresponding to WO 2005/044968 A1), the applicant, too, discloses water-soluble cleaning and disinfecting agents containing permanganate, wherein, in addition to permanganate, a second oxidizing agent is used, which sometimes serves as a main oxidizing agent while permanganate mainly functions as an indicator.
In many cases, for example, when using permanganate as the only oxidizing agent, i.e. at high concentrations of the indicator, it is difficult to determine via the color change if there are still oxidizable residues in the system, so that frequently more cleaning solution than necessary is used.
For solving this problem, DE 10 2006 060 204 A1 proposes, for example, a cleaning method comprising recycling of the indicator agent for reuse as an oxidizing agent. The preferred cleaning and indicator agents mentioned are the same as disclosed in the applications of the applicant cited above. In preferred embodiments, DE 10 2006 060 204 A1 provides for the measurement of a color value of the cleaning composition after exiting the system and comparing it with the color value before entering the system. As soon as the values are substantially matching, e.g. within a certain tolerance range, the system may be regarded as sufficiently cleaned. If not, one or more cleaning steps have to be repeated, as disclosed in paragraph [0020], which implies that this is a discontinuous cleaning method that is interrupted by passing an indicator solution through the system. For determining the color value, for example, a digital camera may be used, e.g. a so-called “Photo Eye” of the applicant.
The disadvantage of such a method according to DE 10 2006 060 204 A1 is that the values to be compared, i.e. the color value measured after exit from the system to be cleaned and the reference value of the indicator agent before entering the system, are measured under different conditions, as is explained in more detail below, so that they are not directly comparable. The present invention is aimed at solving this problem.